Bidirectional Electron Transfer Capability in Phthalocyanine–Sc₃N@<i>I</i>_<i>h</i>–C₈₀ Complexes

To activate oxidative and/or reductive electron transfer reactions, <i>N</i>-pyridyl-substituted Sc₃N@<i>I</i>_<i>h</i>–C₈₀ (<b>4</b>) and C₆₀ (<b>3</b>) fulleropyrrolidines have been prepared and axially coordinated to electron-rich (<b>1</b>) or electron-deficient (<b>2</b>) Zn­(II)­phthalocyanines (Zn­(II)­Pcs) through zinc-pyridyl, metal–ligand coordination affording a full-fledged family of electron donor–acceptor ensembles. An arsenal of photophysical assays as they were carried out with, for example, <b>1</b>/<b>4</b> and <b>2</b>/<b>4</b> show unambiguously that a Zn­(II)­Pc-to-Sc₃N@<i>I</i>_<i>h</i>–C₈₀ photoinduced electron transfer takes place in the former ensemble, whereas a Sc₃N@<i>I</i>_<i>h</i>–C₈₀-to-Zn­(II)­Pc electron transfer occurs in the latter ensemble. To the best of our knowledge, this is the first time that a fullerene-based molecular building block shows an electron transfer dichotomy, namely acting both as electron-acceptor or electron-donor, and its outcome is simply governed by the electronic nature of its counterpart. In light of the latter, the present work, which involves the use of Sc₃N@<i>I</i>_<i>h</i>–C₈₀, one of the most abundant and easy-to-purify endohedral metallofullerenes, is, on one hand, a paradigmatic change and, on the other hand, an important milestone <i>en-route</i> toward the construction of easy-to-prepare molecular materials featuring switchable electron transfer reactivity

Subphthalocyanines Axially Substituted with a Tetracyanobuta-1,3-diene–Aniline Moiety: Synthesis, Structure, and Physicochemical Properties

A 1,1,4,4-tetracyanobuta-1,3-diene (TCBD)–aniline moiety has been introduced, for the first time, at the axial position of two subphthalocyanines (SubPcs) peripherally substituted with hydrogen (H₁₂SubPc) or fluorine atoms (F₁₂SubPc). Single-crystal X-ray analysis of both SubPc–TCBD–aniline systems showed that each conjugate is a racemic mixture of two atropisomers resulting from the almost orthogonal geometry adopted by the axial TCBD unit, which were separated by chiral high-performance liquid chromato­graphy. Remarkably, the single-crystal X-ray structure of one atropisomer of each SubPc–TCBD–aniline conjugate has been solved, allowing to unambiguously assign the atropisomers’ absolute configuration, something, to the best of our knowledge, unprecedented in TCBD-based conjugates. Moreover, the physicochemical properties of both SubPc–TCBD–aniline racemates have been investigated using a wide range of electrochemical as well as steady-state and time-resolved spectroscopic techniques. Each of the two SubPc–TCBD–aniline conjugates presents a unique photophysical feature never observed before in SubPc chemistry. As a matter of fact, H₁₂SubPc–TCBD–aniline showed significant ground-state charge transfer interactions between the H₁₂SubPc macrocycle and the electron-withdrawing TCBD unit directly attached at its axial position. In contrast, F₁₂SubPc–TCBD–aniline gave rise to an intense, broad emission, which red shifts upon increasing the solvent polarity and stems from an excited complex (i.e., an exciplex). Such an exciplex emission, which has also no precedent in TCBD chemistry, results from intramolecular interactions in the excited state between the electron-rich aniline and the F₁₂SubPc π-surface, two molecular fragments kept in spatial proximity by the “unique” three-dimensional geometry adopted by the F₁₂SubPc–TCBD–aniline. Complementary transient absorption studies were carried out on both SubPc–TCBD–aniline derivatives, showing the occurrence, in both cases, of photoinduced charge separation and corroborating the formation of the aforementioned intramolecular exciplex in terms of a radical ion pair stabilized through-space

Long-Range Orientational Self-Assembly, Spatially Controlled Deprotonation, and Off-Centered Metalation of an Expanded Porphyrin

Expanded porphyrins are large-cavity macrocycles with enormous potential in coordination chemistry, anion sensing, photodynamic therapy, and optoelectronics. In the last two decades, the surface science community has assessed the physicochemical properties of tetrapyrrolic-like macrocycles. However, to date, the sublimation, self-assembly and atomistic insights of expanded porphyrins on surfaces have remained elusive. Here, we show the self-assembly on Au(111) of an expanded aza-porphyrin, namely, an “expanded hemiporphyrazine”, through a unique growth mechanism based on long-range orientational self-assembly. Furthermore, a spatially controlled “writing” protocol on such self-assembled architecture is presented based on the STM tip-induced deprotonation of the inner protons of individual macrocycles. Finally, the capability of these surface-confined macrocycles to host lanthanide elements is assessed, introducing a novel off-centered coordination motif. The presented findings represent a milestone in the fields of porphyrinoid chemistry and surface science, revealing a great potential for novel surface patterning, opening new avenues for molecular level information storage, and boosting the emerging field of surface-confined coordination chemistry involving f-block elements